At the time microwave popcorn was first commercialized, microwave popcorn bags were sized to be the largest size that would fit in the most commonly available ovens in use at the time. A de facto standard size of about 100 grams resulted. This size has come to be preferred by microwave popcorn customers, with sizes larger, and especially smaller, being much less acceptable as shown by relative sales volume.
This size fits and works well in most of today's microwave ovens. However, there is one class of oven where this size does not work well--and that is the class of oven wherein a turntable is used to enhance uniformity of heating. In such ovens, if the 100 gram bag is too close to the maximum space capacity of the oven, the bag can catch or hang up and so no longer rotate, thus inactivating the uniformity of heating feature of the oven turntable, resulting in reduced pop volume and sometimes even scorching. Such small ovens may often have a turntable of about 23 cm or less in diameter and are very common in some markets, making it unfeasible to market the most popular bag size in those markets. In fact, the largest de facto standard size that will fit these ovens is the 50 gram size, which uses a bag having a height of only about 23 cm and a width of about 10 cm across each face.
Another problem in certain microwave ovens is that the area of maximum field intensity is in an unusual position owing to the design of the oven cavity or the presence of a metal cooking surface. For example, in a typical Japanese oven it has been found that the maximum field intensity is not located at or immediately above the support surface within the oven as it is in typical U.S. ovens. Japanese ovens are characterized by the presence of a metal cooking surface, i.e., a metal support surface such as a turntable for the food at the bottom of the oven compartment. Foods like popcorn which depend on an electric field powered susceptor in the bottom of a paper container, e.g., a bag, are not heated very well in ovens of this kind. As a result, the popcorn pops slowly, and very often popping is incomplete, resulting in a large number of unpopped kernels which consumers find unacceptable. In addition, heating may be spotty, causing popcorn in some parts of the bag to burn or kernels in other portions of the package remain unpopped. This is a particularly serious problem to the consumer who often perceives the packaged popcorn as a poor product and may never buy it again. By contrast, other ovens such as those commonly marketed in the United States exhibit a maximum microwave field intensity that is positioned very close to the cooking surface (the oven floor), e.g., about one-sixteenth to about one-eighth inch above the cooking surface so that the microwave energy is transmitted very efficiently to the susceptor of a packaged food product resting directly on the floor of the oven.
A major objective of the present invention is to provide an improved microwave popcorn popping bag in which energy can be transmitted efficiently to the susceptor in both of the above types of ovens. A more specific objective is to find a way of mass producing an inexpensive disposable paper bag that can be placed selectively in either of two or more positions within the microwave oven to assure popping at maximum efficiency. Another more specific object is to provide an inexpensive popcorn bag that can be mass produced efficiently and in which cooking can be carried out in either a raised or a lowered position.
These and other more detailed and specific objects of the invention will be better understood by reference to the following detailed description and figures which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.